1. Field of the Invention
The present invention relates to apparatuses for cooling hot bulk coke by indirect heat exchange with a coolant such as water.
2. Description of the Prior Art
Coke is a porous carbon substance which is a useful by-product of the destructive distillation of coal or petroleum. In the production of coal gas, for example, hot coke is a by-product which must be cooled. A variety of methods and devices are available in the prior art for cooling hot glowing bulk coke discharged during distillation of coal or petroleum. Generally these cooling apparatuses involve a cylindrical drum rotating in a cooling bath, the drum holding the material to be cooled. The drum has means within it or is so mounted that the coke moves from an inlet end, the "hot end," to an outlet end, the "cold end." Temperatures at the hot end may be relatively high, such as 1400.degree. C. while at the cold end relatively low, such as about 65.degree. C.
We are aware of a variety of direct heat exchange devices such as those disclosed in United States Pat. No. 2,840,922; 2,841,883; and 3,050,868; but the prior art indirect heat exchange devices disclosed in U.S. Pat. No. 2,884,229; 2,899,176; and 3,917,516 are the closet prior art to our invention we are aware of. In addition to providing a cooling apparatus, each of the indirect heat exchangers in these references attempts to solve the problems associated with the intense heat encountered in cooling hot bulk material such as coke. None of their solutions is satisfactory.
In U.S. Pat. No. 2,884,229 longitudinally oriented hollow tubes with coolant flowing though them are used for indirect heat exchange. The tubes are shown to be of a consistent diameter, thickness and material composition throughout their length. In order to provide further cooling, a separate scoop is added at the end of each hollow tube to introduce more coolant into the tube. The addition of these scoops is expensive and inefficient and does not serve to reduce the wear of the hollow tubes at the inlet end of the drum due to the high temperature of the hot glowing coke nor do the scoops reduce damage at the outlet end of the tubes caused by the cooled coke which has hardened and so is highly abrasive.
In U.S. Pat. No. 2,899,176 crescent-shaped hollow "flights" are employed as the indirect heat exchange elements. The flights are disposed through the rotating drum. Coolant flows through the flights and hot coke in the interior of the drum is contacted by the cooled interior surface of the flights. The flights are disclosed as having consistent thickness and dimensions throughout. The flights also are positioned so that they act as a internal conveying screw for the hot coke to move it from the hot end to the cold end of the drum. In order to provide an increase in heat exchange capability, each flight has an adjustable orifice which can be opened to permit more coolant to flow through the flight or to permit the coolant to flow more quickly through the flight. This adjustability feature, however, is not satisfactory for reducing the wear on the flights at the hot end of the cooler due to the high inlet temperature; nor does this adjustability feature have a salutary effect on the flights at the cold end of the cooler which are worn down by the abrasive action of the coke.
The cooler of U.S. Pat. No. 3,917,516 uses a plurality of cooling pockets as indirect heat exchange devices. Although this patent recognizes the problems associated with the substantial temperature differentials between both the exterior and interior of the rotating drum and the hot end and cold end of the drum, as well as the wearing problems of the pockets themselves, its solution of simply increasing material thickness in selected areas has not solved these problems in a satisfactory and practical manner.
The solution of U.S. Pat. No. 3,917,516 includes increasing the wall thickness of the rotating drum at the hot end to better withstand the high inlet temperature and increasing the wall thickness at the outlet end to better withstand the abrasive effect of the cooled coke. The fabrication of such a drum with thickness varying outwardly from an intermediate region to both ends is a significantly more complex and more expensive procedure than the fabrication of drums of other configurations. Also, when even the thickened portions wear out of wear through, a significant amount of downtime is required to replace or rebuild the worn parts, resulting in production losses.
U.S. Pat. No. 3,917,516 also proposes cooling pockets varying in height and width, depending on where they are located in the drum and, to protect the surfaces of the pockets turned towards the axis of the drum, angled metal aprons are attached to the pocket's surface. The pockets are disclosed as being of varying thicknesses depending on relative location in the drum. Since the material composition of the pockets does not vary no matter how thick they are, this approach attempts to solve both high temperature problems and abrasion problems by using more and more of the same material without regard for its suitability for solving one problem or the other.